An ocean installation, such as an offshore platform for exploration and production of carbon hydrates, may experience high winds, large waves, and strong currents in its service life. This activity can also cause an oil spill. Coastal areas of continents are under the threat of tsunamis (as a result of an earthquake or a volcano eruption, e.g.), especially those regions surrounding the Pacific Ocean and the Indian Ocean. Harbors and low lying areas on coasts are prone to storm surge, such as the cities of New Orleans and Galveston in the United States. Man-made structures are used to mitigate the forces of the nature in some of the examples enumerated above.
Breakwaters, installed in shallow water and close to the coastal areas, are used to reduce the intensity of wave action, and therefore to reduce coastal erosion. Levees are used to prevent floods from, e.g., a storm surge. Oil booms have been used at a large scale, to contain oil spills.
Wave dampers are used to alleviate the strength of the wave forces in laboratories. In a wave basin, the wave dampers, consisting of layers of porous screens and located at one end, absorb the waves generated by wave makers at the opposite end. This way, the progressive waves generated at one end will reach the other with minimum reflection, so that ocean waves can be more realistically simulated. A study by Thomson indicated that with two layers of porous screens, 80% of wave transmission can be eliminated. Molin and Fourest studied the quantitative relation between wave absorption and the number of screens.
In an open ocean, winds, waves, and currents often act simultaneously. The wave dampers used in a laboratory, if installed offshore, can dampen the forces from all these disturbances. These dampers can also be designed to act as barriers to contain crude oil on the sea surface, in case of an oil spill. The issue is to have a support structure, in shallow and in deep water, on which the barriers can be mounted. The support structures must have minimum motions themselves in winds, waves, and currents.
If the water is not deep, say, less than 500 feet, a fixed platform concept can be used to support the barriers. However, very often there is a need to use barriers in a deep ocean, where the water depth is over 1,000 feet. One example is to dampen the tsunami waves, which have a smaller wave height in deepwater (about 3 to 6 feet), while these waves can reach over 30 feet or greater when they land on shore. Another example is the need to protect deepwater oil platforms, which are regularly operating at a water depth of over 5,000 feet. Floating barriers, if installed surrounding these platforms, can alleviate the environmental loads and barricade an oil spill, should it occur.
Over the past 40 years, floating structures at great ocean depth have been installed to explore and to produce carbon hydrates. New floating structure concepts also emerge. One of them is the fully constrained platform abbreviated as FCP shown and described in my copending U.S. patent application Ser. No. 13/084,788, which is hereby incorporated herein in its entirety. Referring now to FIG. 1 for the fully constrained platform concept hereinafter abbreviated as “FCP”, a buoyant, surface structure FCP is constrained with a tether system 12 vertically and angularly. The tethers 12 are anchored on the seabed. The buoyancy generated by the buoyant surface structure FCP is larger than its weight. The excessive lift force is taken by the tether system 12, which will compensate for the payloads. A key feature of a FCP is that its motion is constrained in all six degrees of freedom, namely, surge, sway, heave, roll, pitch, and yaw, so that it will have minimal motion under environmental loads.
No known floating barriers have been permanently installed in deep oceans at a large scale. There is clearly a need in the art to alleviate winds, waves, and currents in an open ocean, in a gulf or in a bay, or to barricade an oil spill. The present invention discloses methods and apparatus for such a purpose.